This application claims priority to U.S. provisional application 60/277,277, filed Mar. 21, 2001, herein incorporated by reference.
1. Field of the Invention
This invention relates to a fabric having fire blocking properties. The fabric is suited for use in many fire blocking applications, including as a fire blocking layer in aircraft seats, where it may be positioned between an outer dress covering and an inner foam core, so as to cover and protect the foam core. The fabric is also suited for automotive, bus, rail, or recreational vehicle applications.
2. Description of the Related Art
Title 14 of the U.S. Code of Federal Regulations contains the rules adopted by the Federal Government related to aviation and space. Federal aviation regulations related to airworthiness standards for transport category airplanes are contained in Part 25 of Title 14. Of particular interest in aircraft seating are rules and testing standards regarding aircraft compartment interiors, contained in Part 25.853 and Appendix F to Part 25 (2001). These rules pertaining to the flammability of cabin materials, herein incorporated by reference, are designed to minimize the loss of human life in the event of a post-crash fire.
In aircraft seating, the amount of protection that a fire blocking fabric must provide depends on the nature of the foam seat cushion it covers and on the outer dress cover material used, as disclosed for example in U.S. Pat. No. 4,750,443, herein incorporated by reference. Fabricated polyurethane cushions may require an additional level of protection compared with less dense molded cushions. The dress cover may be manufactured of a woven wool/nylon blend, woven nylon, or leather-covered. Of these, a 90%/10% wool/nylon blend is commonly used and requires the least amount of fire protection. Nylon dress coverings require additional protection, and leather-covered seats require the most fire protection.
An example of a commercially available fire blocking fabric is manufactured by Tex Tech Industries of North Monmouth, Me., and is available as Style #XD192:19R. This fabric has a mass per unit area of 10.0 oz/yd2, and a thickness of 0.060 inches. The fabric is composed of at least 2 layers of nonwoven batts consisting of 100% polybenzimidazole (PBI) staple fibers, and a woven supporting scrim consisting of staple meta-aramid fibers and having a mass per unit area of 2.2 oz/yd2.
This particular fabric is a superior fire blocker and meets Federal Aviation Administration (FAA) regulations concerning flame resistance in accordance with Federal Aviation Regulation (FAR) 25.853 and Appendix F to Part 25 for virtually all dress covers. Its performance is excellent in protecting leather-covered seats typically found in first class and crew seating applications. However, it is extremely costly to manufacture due to its weight and the high cost of its materials of construction.
Due to the high cost of PBI staple fibers, this particular fabric is not used on seats having the most common wool/nylon blend dress covers, as it provides far greater protection to the foam core of the seat cushion than is required by FAA regulations.
U.S. Pat. No. 5,534,325 (Jorder, et al.), herein incorporated by reference, discloses a flame barrier comprising nonwoven fabric containing staple fibers made of phenolic resin, para-aramid or melamine resin, alone or in combination with 20 to 60 percent by weight pre-oxidized polyacrylonitrile (pre-ox PAN). The fabric also contains 15 to 30 percent by weight vermiculite, an inorganic filler, dispersed throughout its volume. Para- or meta-aramid filaments can be anchored in the nonwoven fabric with a tricot weave or using a stitchbonding process, described in U.S. Pat. No. 5,279,878, also incorporated by reference herein. However, the process of dispersing vermiculite in a nonwoven fabric is difficult, costly, and hard to control and loose particles of vermiculite may pose a concern after extended seat wear.
U.S. Pat. No. 4,540,617 (Kawanishi et al.), herein incorporated by reference, discloses a woven fabric of semi-carbon fibers and para-oriented aromatic polyamide having a silicone resin coating on at least one surface. The coating also contains inorganic filler. Typically, coated fabrics like the one disclosed in this patent evolve amounts of smoke and fumes which may be toxic to passengers in a cabin fire. The coating also adds additional expense to the product.
An object of the present invention is to provide a less expensive fire-blocking fabric that meets Federal Aviation Administration regulations for flammability resistance in accordance with FAR 25.853 and Appendix F to Part 25, regardless of the seat cushion and dress cover construction.
A further object is to provide a more durable fabric that exceeds established mechanical wear resistance requirements of Boeing Aircraft Company standard BSS 7302 Seat Wear Test for Upholstery Fabrics and Fireblocking Layers, commonly known as the xe2x80x9cSquirmin"" Hermanxe2x80x9d test.
Yet another object is to provide a fabric having some water and stain repellency.
Preferred fire blocking fabrics according to the invention comprise about 10 to about 90 percent by weight para-aramid fibers and about 10 to about 90 percent by weight preoxidized polyacrylonitrile fibers (pre-ox PAN) in a needlepunched nonwoven layer.
The nonwoven needlepunched fabric layers according to the invention may also include up to about 35 percent by weight of recycled polybenzimidazole, para-aramid, meta-aramid fibers, or combinations thereof (garnett). A garnett is a staple length or chopped fiber recovered from fabric or yarn via a coarse carding operation. Carding, in turn is a process by which staple fibers are sorted, separated and partially aligned.
In preferred embodiments, the nonwoven needlepunched fabric layers according to the invention contain in the range of about 30-60 percent by weight staple para-aramid fibers, in the range of about 10-40 percent by weight pre-ox PAN, and in the range of about 5 and about 35 percent by weight of a garnett comprising recycled polybenzimidazole, para-aramid, meta-aramid fibers, or combinations thereof.
The fireblocking fabric according to the invention may comprise a single batting layer of the above-described nonwoven material or two or more such batting layers stitched or otherwise mechanically held together. The batting layers each have a weight in the range of about 1.0 to about 12.0 ounces per square yard. The thickness of the finished fabric in either case ranges between about 0.020 inches up to about 0.150 inches and has a mass per unit area between about 3.0 and about 14.0 ounces per square yard.
In preferred embodiments the above-described nonwoven fabric is combined with a relatively loosely woven scrim on one side to make a fire blocking fabric. In some instances two adjacent layers of woven scrim having a different composition can be used, such as a woven glass and a polyester. In some instances, layers of scrim can be incorporated between nonwoven fabric layers in the finished fire blocking fabric.
Preferred nonwoven fabric layers and finished fire blocking fabrics according to the invention generally meet the standards of flame resistance set forth in FAR 25.853 without added flame resistant coatings (such as silicone resin coatings), or the addition of inorganic fillers. In particularly preferred embodiments, the nonwoven fabrics according to the invention do not contain inorganic fillers. However, in preferred embodiments, a fluoropolymer coating on the fabric, or on the individual fabric layers, imparts water repellency and stain-proofing.
Further objects and advantages of this invention will become apparent from a consideration of the drawings and description of the preferred embodiments.